Foul body odor from rectum?

I’m 24 and male…I’m very clean and shower daily. But I have weird condition started when I was teen. I have a foul body odor that smells like feces, rotten egg, garbage and sometimes like gasoline. The smell seems to come out from my rectum. It’s on and off thing. It’s affecting my social life and I did see a doctor but they don’t seem to understand the cause. When I’m in a car with a/c on it seems that I smell the odor. I have no leakage or anything like that.